Heat exchangers

ABSTRACT

A heat exchanger which may be used in an engine, such as a vehicle engine for an aircraft or orbital launch vehicle. is provided. The heat exchanger may be configured as generally drum-shaped with a multitude of spiral sections, each containing numerous small diameter tubes. The spiral sections may spiral inside one another. The heat exchanger may include a support structure with a plurality of mutually axially spaced hoop supports, and may incorporate an intermediate header. The heat exchanger may incorporate recycling of methanol or other antifreeze used to prevent blocking of the heat exchanger due to frost or ice formation.

CROSS-REFERENCE TO RELATED APPLICATIONS

This Application is a Division of U.S. Application Serial No.17/316,538, filed May 10, 2021, which is a Continuation of U.S. Pat.Application No. 14/296,603, filed on Jun. 5, 2014, which claims priorityunder 35 U.S.C. § 119(a) to United Kingdom Patent Application Nos. GB1318098.9, GB 1318109.4, GB 1318100.3, GB 1318107.8, and GB 1318099.7,each filed on Oct. 11, 2013. Each of the aforementioned U.S. and UnitedKingdom patent applications is hereby incorporated by reference herein.

FIELD

The present invention relates to heat exchangers such as of the typewhich may be used in aerospace applications or in industrial or otherapplications. The invention also relates to engines such as aircraft oraerospace engines including such heat exchangers and to aircraftincluding such heat exchangers or engines.

BACKGROUND

GB-A-2241319 discloses a heat exchanger with inter-nested spiral tubesections. An inlet manifold is located on one wall and an outletmanifold is located on another wall at the end of the apparatus.However, it is difficult to build such a heat exchanger which will besubject to considerable temperature variations and in a form capable ofenduring the numerous cycles that are desirable in certain heatexchangers such as when used in reusable vehicles.

Also, with a substantial airflow through the heat exchanger radiallypast the tubes, the drag of the airflow on the tubes produces a highradial force on the tubes and the tubes are difficult to support andmake last a long time. Additionally, the heat exchanger has ratherlimited cycle functionality and it is difficult to configure heatexchangers, to accommodate them in an engine and provide a system withlow weight and low pressure drop. Also, to achieve sufficientperformance it has proven necessary to design a cycle which coolsatmospheric air before it enters a compression section downstream ofsuch a heat exchanger at a temperature below 0° C. This canunfortunately very easily result in a very rapid blocking of the heatexchanger with ice because there is often a considerable amount of watervapour in the lower atmosphere where the launch of a vehicle containingthe heat exchanger for air cooling may take place, making the entirevehicle unviable. This has proven an exceptionally difficult problemwhich has been looked at for many years and has been a significanthurdle in being able to provide a reusable vehicle which can operate ina relatively economical horizontal take-off air-breathing mode, andeither continue, such as the LAPCAT vehicle which is intended to becapable of transporting three hundred passengers from Brussels, Belgiumto Sydney, Australia in about 4.6 hours in an approximately Mach 5cruising mode, or switch, like the SKYLON vehicle, into a rocket modefor travel out of the atmosphere into orbit.

GB-A-2241537 discloses an air intake for aerospace propulsion whichincludes a first heat exchanger for cooling incoming air, a waterseparator downstream of the first heat exchanger, a liquid oxygeninjector downstream of the water separator and a second heat exchangerdownstream of the liquid oxygen injector. The injector reduces theairflow temperature so that water remaining in the airflow downstream ofthe water separator is converted to small dry ice crystals. Thestructure requires the use of two entirely separate heat exchangers andtakes up a very considerable axial distance in a flow path along a ductbetween the two heat exchangers. Also, the liquid oxygen is used toreduce the temperature of the flow from between 5° and 13° C. to minus50° C. or lower, such that a considerable amount of liquid oxygen needsto be used, to cool the air in a duct where there is already aircontaining oxygen which may be used downstream in the propulsion.

SUMMARY

According to a first aspect, there is provided a heat exchanger havingat least one first conduit section for the flow of a first fluid in heatexchange with a second fluid in a flow path which passes the at leastone first conduit section, and a support for the at least one firstconduit section, wherein the at least one conduit section is mounted ata first location to the support, and in which the at least one conduitsection at a second location thereon is movable relative to the supportin response to thermal change.

Optionally, the at least one first conduit section includes a pluralityof tubes for heat exchange.

Optionally, the tubes are connected at a first end thereof to an inletheader and at a second end thereof to an outlet header of the at leastone first conduit section.

Optionally, said first location is at one of the headers, which isfixedly mounted to the support, the other of the headers being movablerelative to the support in response to thermal change.

Optionally, the other of the headers is mounted to a movable supporttherefor which is movable relative to said support.

Optionally, each said first conduit section comprises a spiral sectionhaving a plurality of the tubes extending along in a spiral shapealongside and spaced from one another in rows.

Optionally, the tubes in said first conduit section are arranged inbetween 1 and 40 rows spaced from one another in a radial direction, forexample 4 such rows.

Optionally, the tubes are arranged in about 10 to 1000 rows spaced fromone another in an axial direction, for example about 70 to 100 suchrows.

Optionally, the tubes are about 2 to 3 metres long and extend from afirst header to a second header.

Optionally, the tubes have a diameter which is about 1 mm.

Optionally, the tubes have a wall thickness of about 20 to 40 microns.

Optionally, a plurality of said spiral sections are inter-nested withand oriented angularly spaced relative to one another.

Optionally, said spiral sections are configured in the shape of agenerally cylindrical drum.

Optionally, the support includes at least one circular hoop to whichsaid first conduit is secured.

Optionally, the support includes a plurality of said circular hoopswhich are configured spaced apart from one another in a generallycylindrical perforated drum structure and in which a header of saidfirst conduit is fixed to a plurality of said circular hoops.

Optionally, the heat exchanger includes a support structure extending inan annular fashion and at least partly radially between said header anda further header of the respective at least one first conduit, thefurther header being supported by a guide member arranged to movecircumferentially relative to the perforated drum structure in responseto thermal change.

Optionally, said header is rigid or substantially rigid and is fluidlycoupled to a flexible conduit.

Optionally, the flexible conduit is fluidly coupled to a rigid orsubstantially rigid manifold.

Optionally, the manifold is fixed axially in position relative to thesupport but free to move, e.g. grow, radially.

Optionally, the rows of tubes in a said first conduit section comprise aplurality of rows spaced from one another by spacers arranged to counteraerodynamic load applied to the tubes.

Optionally, a load element, such as a shim, is provided between tubes oftwo adjacent said first conduit sections for transmitting loadtherebetween while allowing relative sliding motion therebetween inresponse to thermal change.

Optionally, the load element is substantially aligned with the spacersto form a generally radially extending load path structure for reactionagainst aerodynamic load applied to the tubes while allowing relativemovement between adjacent said first conduit sections in response tothermal change.

Optionally, said heat exchanger includes a plurality of said load pathstructures configured in a series in which they are spaced generallycircumferentially from one another.

According to a second aspect, there is provided a vehicle engineincluding a combustion section and a heat exchanger according to thefirst aspect with or without any optional feature thereof, adapted tocool air (as the second fluid) in a flow path directed towards thecombustion section.

Optionally, said vehicle engine includes a helium supply for providinghelium as the first fluid, or another working fluid such as hydrogen.

According to a third aspect, there is provided a flying machine, such asan aircraft or orbital launch vehicle, which includes a heat exchangeraccording to the first aspect with or without any optional featurethereof.

According to a fourth aspect, there is provided a flying machine, suchas an aircraft or orbital launch vehicle, which includes an engineaccording to the second aspect with or without any optional featurethereof.

According to a fifth aspect, there is provided a heat exchanger having aplurality of first conduit sections for the flow of a first fluid inheat exchange with a second fluid in a flow path which passes the firstconduit sections, and a support for the plurality of first conduitsections, each of the first conduit sections comprising a plurality oftubes for heat exchange, each first conduit section comprising a spiralsection having a plurality of the tubes extending along in a spiralshape alongside and spaced from one another in rows, wherein at leastone load element is provided between tubes in mutually radially spacedrows for countering aerodynamic load applied to the tubes.

Optionally, said load element comprises a spacer fixing together, suchas by brazing, tubes in radially spaced rows.

Optionally, said load element comprises an element, such as a shim,provided between tubes of two adjacent said first conduit sections fortransmitting load therebetween while allowing relative sliding motiontherebetween in response to thermal change.

Optionally, said element is fixed to a tube in one said first conduitsection and slidably engages a further said first conduit section.

Optionally, said load element comprises at least one I-beam-shapedelement.

Optionally, the tubes in a said first conduit section are arranged inbetween 1 and 40 rows spaced from one another in a radial direction, forexample 4 such rows.

Optionally, said tubes are about 1 to 3 metres long from a first headerto a second header.

Optionally, the tubes have a diameter which is about 1 mm.

Optionally, the tubes have a wall thickness of about 20 to 40 microns.

Optionally, the tubes are arranged in about 10 to 1000 rows spaced fromone another in an axial direction, for example about 70 to 100 or 70 to200 or 500 such rows.

In some embodiments tubes are made at least partly of alloy material,such as Nickel alloys or Aluminium alloys. Optionally, each tubecomprising a first portion made of a first material and a second portionmade of a second material. The first portion may terminate at one end ofsuch a tube, such as at a header and the second portion may terminate ata second end of such a tube as at a further header. The first and secondportions may be connected to one another such as by a sleeve. This mayenable temperature capability to be increased by the use of a firstmaterial at a relatively hot region of the heat exchanger but a secondmaterial for reasons of density or lost to be used in a colder region.

For example, an aluminium alloy may be used in a colder region and aceramic or heat resistant alloy in a hotter region. Each of the firstand second portions may be connected at one end thereof to theintermediate header.

Optionally, the plurality of spiral sections are inter-nested with andoriented angularly spaced relative to one another.

Optionally, said spiral sections are configured in the shape of acylindrical drum.

Optionally, the support includes at least one circular hoop to which afirst said conduit is secured.

Optionally, the support includes a plurality of said circular hoopswhich are configured spaced apart from one another in a generallycylindrical perforated drum structure, and in which at least onelongeron member is provided for engagingly supporting an adjacent saidtube at a location substantially radially aligned with at least one saidload element.

Optionally, a plurality of said load elements are provided in agenerally radially extending load path structure for reaction againstaerodynamic load applied to the tubes.

Optionally, the load path structure is adapted to permit relativemovement between tubes of adjacent first said conduit sections inresponse to thermal change.

According to a sixth aspect, there is provided a vehicle engineincluding a combustion section and a heat exchanger according to thefifth aspect with or without any optional feature thereof, adapted tocool air, as the second fluid, in a flow path directed towards thecombustion section.

Optionally, said vehicle engine includes a helium supply for providinghelium as the first fluid.

According to a seventh aspect, there is provided a flying machine, suchas an aircraft or orbital launch vehicle, which includes a heatexchanger according to the fifth aspect of the invention with or withoutany optional feature thereof.

According to an eight aspect, there is provided a flying machine, suchas an aircraft or orbital launch vehicle, which includes an engineaccording to the sixth aspect with or without any optional featurethereof.

According to a ninth aspect, there is provided a heat exchanger havingat least one first conduit section for the flow of a first fluid in heatexchange with a second fluid in a flow path which passes the at leastone first conduit section, in which each first conduit section comprisesa flow path via at least one tube from an inlet to an outlet, and inwhich an intermediate header is provided in the flow path between theinlet and outlet for flow communication with an intermediate fluid flowpath.

Optionally, each of the inlet and outlet comprises a header tube.

Optionally, the header tubes are straight.

Optionally, the at least one first conduit section includes a pluralityfirst flow tubes extending from the inlet to the intermediate header forflow therebetween and a plurality of second flow tubes extending fromthe intermediate header to the outlet for flow therebetween.

Optionally, the length of a first flow tube plus the length of a secondflow tube is about 2 to 3 metres.

Optionally, the first flow tubes and/or the second flow tubes are about1 mm in diameter.

Optionally, the first flow tubes and/or the second flow tubes have wallthickness of about 20 to 40 microns.

Optionally, said first conduit section comprises a spiral section havingthe first and second flow tubes extending in a spiral shape alongsideand spaced from one another in rows.

Optionally, said heat exchanger includes a controller for controllingpressure in the intermediate flow path.

Optionally, the controller includes a flow valve.

Optionally, the intermediate header comprises an outer enclosure forenclosing first fluid and an injector for injecting intermediate fluidflow into the outer enclosure.

Optionally, the injector comprises a tube having a series of flowapertures spaced therealong for injecting fluid into the outerenclosure.

Optionally, each of the outer enclosure and the injector comprises astraight elongate tube.

Optionally, said rows include a plurality of rows spaced apart from oneanother along the longitudinal direction of the outer enclosure, thetubes in said spaced apart rows being fluidly coupled to the outerenclosure at respective spaced locations along the length thereof.

In some embodiments tubes are made at least partly of alloy material,such as Nickel alloys or Aluminium alloys. Optionally, each tubecomprising a first portion made of a first material and a second portionmade of a second material. The first portion may terminate at one end ofsuch a tube, such as at a header and the second portion may terminate ata second end of such a tube as at a further header. The first and secondportions may be connected to one another such as by a sleeve. This mayenable temperature capability to be increased by the use of a firstmaterial at a relatively hot region of the heat exchanger but a secondmaterial for reasons of density or lost to be used in a colder region.

For example, an aluminium alloy may be used in a colder region and aceramic or heat resistant alloy in a hotter region. Each of the firstand second portions may be connected at one end thereof to theintermediate header.

A tenth aspect provides a heat exchanger having at least one firstconduit section for the flow of a first fluid in heat exchange with asecond fluid in a flow path which passes the at least one first conduitsection, in which each first conduit comprises a flow path via at leastone tube from an inlet to an outlet, wherein at least one of said tubeshas first and second portions extending therealong which are formed ofdifferent materials to one another.

According to an eleventh aspect, there is provided a method of operatinga heat exchanger according to the ninth aspect with or without anyoptional feature thereof, which comprises flowing helium through the atleast one first conduit and through the intermediate fluid flow path.

Optionally, said method of operating a heat exchanger comprises flowingair as the second fluid in the flow path past the at least one firstconduit.

According to a twelfth aspect, there is provided an engine, such as avehicle engine, including a combustion section and a heat exchangeraccording to the ninth or tenth aspect with or without any optionalfeature thereof, adapted to cool air (as the second fluid) in a flowpath directed towards the combustion section.

Optionally, said engine includes a helium supply for providing helium asthe first fluid.

According to a thirteenth aspect, there is provided a flying machine,such as an aircraft or orbital launch vehicle, which includes a heatexchanger according to the ninth or tenth aspect with or without anyoptional feature thereof.

According to a fourteenth aspect, there is provided a flying machine,such as an aircraft or orbital launch vehicle, which includes an engineaccording to the twelfth aspect with or without any optional featurethereof.

According to a fifteenth aspect, there is provided a support structurefor a heat exchanger having at least one first conduit section for theflow of a first fluid in heat exchange with a section fluid in a flowpath which passes the at least one first conduit section, the supportstructure comprising a generally cylindrical perforated drum structure.

Optionally, said support structure includes a plurality of mutuallyaxially spaced hoop supports.

Optionally, said support structure includes a plurality of mutuallyradially spaced longeron members which are adapted to supportinglyengage the said first conduit sections at a generally radially alignedload path structure.

Optionally, the hoop supports are formed with bearers and/or attachmentstructures for locating header tubes of the first conduit sections onthe hoop supports.

Optionally, the hoop supports and longeron members are configured withgenerally rectangular or square flow spaces therebetween.

Optionally, said support structure including at least one diagonallymounted bracing element extending across and within or adjacent at leastone of the spaces, for example diagonally thereacross.

Optionally, each said space has two diagonally mounted said bracingelements configured in an X configuration thereby providing foursubstantially triangular flow apertures in the region of each saidspace.

According to a sixteenth aspect, there is provided a heat exchanger forcooling a fluid in a flow path and containing a component liable tophase change below a temperature thereof, the heat exchanger comprisinga series of tubes for the passage of coolant and an injector forintroducing an anti-freeze component into fluid in the flow path.

Optionally, the injector comprises an antifreeze injector, e.g. arrangedto inject an alcohol, such as a methanol injector arranged forconnection to a source of methanol.

Optionally, said heat exchanger includes a removal arrangement forremoving liquid located within a body of moving fluid within the flowpath.

Optionally, the removal arrangement is located downstream of theinjector.

Optionally, the removal arrangement includes at least one catcherarrangement or element arranged to extend generally transverse to ageneral flow direction of fluid therepast.

Optionally, said heat exchanger includes at least one row of saidcatcher elements.

Optionally, the catcher elements are spaced apart in the row by aspacing distance which is less than the maximum cross-dimension of eachcatcher element in a direction of spacing thereof.

Optionally, the spacing distance is about one quarter, one third or halfof said maximum cross-dimension.

Optionally, the catcher arrangement includes a section row of catcherelements, the second row of catcher elements being staggered (in adirection from one catcher element to another along a row) with thefirst row of catcher elements.

Optionally, the catcher elements in the first and second rows are spacedfrom the catcher elements in the same row substantially the samedistance that they are spaced from the catcher element in the other row.

Optionally, each catcher element has a longitudinal extent and has atleast one point therealong a substantially circular cross section.

Optionally, each catcher element comprises a hollow tube having at leastone (such as a plurality of) liquid collection pocket located on anexterior surface thereof.

Optionally, the hollow tube is hydroformed of metallic material.

Optionally, each liquid collection pocket includes a scavenge aperturecommunicating from the pocket into an interior conduit of the hollowtube, the scavenge aperture area being of small size for limitingairflow drawn thereinto with liquid.

Optionally, said heat exchanger includes a mesh covering each pocketwith a cavity formed between each pocket and the mesh. The mesh may begenerally flat in the region of each pocket. The gap behind each suchportion of mesh provides the cavity. The physical presence of thecatcher element enables air to jig around the catcher element but forliquid to be intertially separated from the air. With the mesh in place,the liquid in the flow may travel into and be caught be the mesh but theair may continue flowing along around the catcher elements.

Optionally, the mesh is an approximately 25 micron to 100 micron mesh,for example a 50 micron mesh.

Optionally, the mesh is coated with a wetting agent.

Optionally, the mesh is coated with silica.

Optionally, said heat exchanger includes a suction system fluidlyconnected to the hollow tube for removing liquid from the collectionpockets.

Optionally, said heat exchanger includes a second said removalarrangement which is located downstream of the said removal arrangement.Embodiments with three of more said removal arrangements are envisagedas well.

The antifreeze injector may include a plurality of injection portionsand may be arranged to inject a more concentrated antifreeze at a firstinjection portion in a first region of air flow and a more diluted (withwater) antifreeze at a second injection portion which is more upstreamthan the first injection portion at a second region of air flow that iswarmer than the first region. The water is obtained by condensation outof the air passing through the heat exchanger due to humidity in theair.

The heat exchanger may include a recycle path for recycling antifreezeand liquid water removed from air flow at the second (or further)removal arrangement for re-injection, upstream of the first removalarrangement, at the second injection portion. Each such re-injection ina plural sequence of such re-injections optionally thus may be with theanti-freeze being more dilute, into warmer air and more upstream in theairflow than upon the previous injection, the anti-freeze thus beingre-injectable along a sequence of re-injection points along a path thatis counter to the direction of air flow through the heat exchanger. Thismay thus be considered a kind of “counterflow” of the antifreezeinjection system even though the antifreeze, upon injection into the airflow, flows along with the air. The reason for the additional dilutionis the condensation of water out of air passing through the heatexchanger. The caught or captured antifreeze (e.g. methanol) and watermay then be re-injected (with the antifreeze thus more dilute) into theair flow at a point further upstream than the previous injection at alocation where the air flow is warmer. This recycling of antifreezeenables sustained operation without having to use too much antifreezesince the same antifreeze may be injected then caught; and it may thenbe re-injected and caught again two or more times dependent upon thenumber of removal arrangements with catcher elements that are employedthrough the heat exchanger. This also allows the methanol content tobecome more and more concentrated as the flow becomes colder.

Optionally, said heat exchanger is adapted to cool air to below 0° C.

Optionally, said heat exchanger is adapted to cool air to or to belowabout minus 100° C., such as down to near minus 140° C., or down to airliquefaction point - about -195° C.

Optionally, said heat exchanger includes a control for controlling theenvironment in the vicinity of the coldest catcher element to be about80 mol % or about 88 wt % methanol (on a water-methanol solid-liquidphase diagram) as temperature approaches about minus 100° C. Theenvironment in the vicinity of the coldest catcher element may as thetemperature approaches or drops below about -100° C. may in someembodiments be about 70 to 90 mol % methanol (on a water methanolsolid - liquid phase diagram), such as about 75 to 85 mol % or 78 to 82mol %.

Optionally, the catcher arrangements are configured and constructed witha sufficient number of catcher elements to remove over 90% of watercontent from air, such as over 95%, about 99% being one example.

According to a seventeenth aspect there is provided a heat exchangerassembly with a longitudinal extent in a longitudinal direction thereofand which comprises at least one generally annular heat exchanger modulearranged to communicate with a longitudinally extending duct, wherein atleast one guide vane is provided for turning flow between one and theother selected from (a) generally radial through the heat exchangermodule and (b) generally longitudinal along the longitudinally extendingduct.

The guide vane may adapted to turn flow from generally radial togenerally longitudinal.

The guide vane may be annular or ring-like.

The guide vane may have a leading edge and a trailing edge and isoptionally of substantially constant thickness between the leading edgeand the trailing edge.

The leading edge may arranged at an angle of about 5 to 20 degreesrelative to a radial direction, e.g. about 10 degrees. This may varyoutside this range in some embodiments.

The trailing edge may be arranged at an angle of about 5 to 15, or about8 to 12, degrees to the longitudinal direction. This may vary outsidethese ranges in some embodiments.

The guide vane may have a longitudinal extent in the longitudinaldirection and the guide vane may comprise a curvedly-flaring leadingsection (which is optionally substantially an arc in cross section) anda substantially conical trailing section, the trailing section extendingfor about 50 to 85% of the longitudinal extent.

The heat exchanger assembly may include a plurality of said guide vaneswhich are optionally arranged in a mutually overlapped series along thelongitudinally extending duct.

The vanes may be arranged with a narrowing therebetween so as toaccelerate flow. In this way flow may be accelerated to substantiallythe same speed at each vane as a bulk exit speed from the longitudinallyextending duct. This assists in maintaining pressure and mass flow rateuniform upstream of the vanes and through the heat exchanger module.

The heat exchanger assembly may include a plurality of said heatexchanger modules arranged in a series along and around saidlongitudinal duct and a series of said guide vanes may be providedextending adjacent and at least substantially the full longitudinalextent of at least one, optionally all, of said heat exchanger modules.This assists in maintaining pressure and mass flow rate uniform upstreamof the vanes and through the heat exchanger modules. Thus two or moregenerally annular said heat exchanger modules may be configured aroundthe longitudinally extending duct and arranged in a series therealong.Flow may pass overall and/or generally inwardly radially through eachheat exchanger module into the longitudinally extending duct. The vanesenable the creation of a generally constant static pressure in the ductdownstream of them and therefore uniform flow is drawn through the heatexchanger modules.

Although the heat exchanger modules may be the same size (includingdiameter or maximum cross-dimension thereof) as one another, they may bedifferent sizes to one another in other embodiments, for example being aseries of generally drum-like arrangements with different diameters toone another. The modules may nevertheless be adapted to operate with thesame mass flux and pressure drop as one another and may include the samenumber of rows of heat exchanger tubes as one another, and may in someembodiments have the same difference outer diameter to inner diameter(of where tubes are in the module).

According to an eighteenth aspect there is provided an engine whichincludes a heat exchanger according to the seventeenth aspect, the heatexchanger being located upstream of an air compressor and/or combustionstage of the engine.

According to an nineteenth aspect, there is provided an engine, such asa vehicle engine, which includes a combustion section and a heatexchanger according to the sixteenth aspect with or without any optionalfeature thereof adapted to cool air in a flow path directed towards thecombustion section.

Optionally, said engine includes a helium supply for providing helium ascoolant flowable through the heat exchanger.

According to a twentieth aspect, there is provided a flying machine,such as an aircraft or orbital launch vehicle, which includes a heatexchanger according to the sixteenth aspect with or without any optionalfeature thereof.

According to an twenty-first aspect, there is provided a flying machine,such as an aircraft or orbital launch vehicle which includes an engineaccording to the eighteenth or nineteenth aspect with or without anyoptional feature thereof.

Thus, in some embodiments the heat exchanger is generally drum-shapedand includes a multitude of spiral sections each containing numeroussmall diameter metal alloy tubes. The spiral sections spiral inside oneanother. The tubes in some examples are each about 2 to 3 metres longand about 1 millimetre in diameter and have a wall thickness of about 20to 40 microns or thereabouts.

Each spiral section has an axially-extending coolant inlet header tubewhich is fixedly attached to a central support sleeve. The tubes of eachspiral section are sealingly connected at one end thereof, such as bybrazing, to the inlet header tube and extend in a small plurality ofrows radially (such as about 1 to 10 rows, 2, 3, 4, 5, 6 or 7 rows beingsome examples) and in a large number of rows axially such as about 75 to100 rows or in excess of 100 rows. These various thin tubes all spiralout from the inlet header tube to an outlet header tube to which theyare also sealingly connected, such as by brazing. In other embodiments,the flow direction could be reversed such that the inlet headers are ata radially outward location and the outlet headers at a radially inwardlocation and air may flow through the heat exchanger in a radiallyoutward direction in a generally counter-flow to the coolant in thetubes which may be helium.

Also, as temperature changes during operation of the heat exchanger orotherwise, the inlet header tubes remain fixed substantially in positionrelative to the internal support sleeve. However, due to the thermalexpansion, the length of the small diameter tubes changes and thevarious spiral sections slide over one another in a generallycircumferential fashion, the outlet header tubes also moving relative tothe internal support sleeve. Therefore, the heat exchanger may bethermally cycled many times due to substantial alleviation of thermalstress, even though over 100 or up to 200 or more full flight cycles.

Also, at various points along their length, the tubes in each spiralsection may be supportingly fixed together such as by brazing and eachrow of tubes which is adjacent to a row of an adjacent spiral sectionmay be provided with a baffle plate, spacer or shim which extends fullyalong the tubes in the axial direction and slightly radiallyapproximately 1 to 10 millimetres or so. The baffle plates or shims inadjacent spiral sections may slideably abut against one another or abaffle plate or shim of one spiral section may slideably engage uponadjacent fluid flow tubes of an adjacent spiral section. Due to thesupporting fixing of the tubes in each section and the sliding abutment,not only are all of the spiral sections easily able to expand andcontract as they desire during thermal cycling but the radial drag loadof heatant such as air, passing through the heat exchanger outside andbetween the small diameter tubes may be transmitted inwardly (oroutwardly) through all of these spiral sections in a strongsubstantially radial load path and may be reacted against by theinternal support sleeve, or by an external support sleeve in the case ofradially outward air flow.

With counter flow heat exchange between radially travelling air flow(heatant) and oppositely radially spiralling helium coolant flow in thenarrow tubes, curved ducting may be provided radially outside the heatexchanger to curve approaching axial air flow into the heat exchanger orexiting axial air flow leaving the heat exchanger in the case ofoutwardly travelling airflow though the heat exchanger. Due to this typeof construction, the heat exchanger tubes are relatively well protectedand in the event of a problem such as bird strike or other ingestioncausing an engine failure after take-off (EFATO), the helium tubes areunlikely to be damaged, the engine may easily be shut down and, with orwithout dumping fuel to come below maximum landing weight, the vehiclemay have a good probability of performing a successful landing with therespective engine shut down.

The internal sleeve may be provided with a perforated or “bird cage”construction to enable the heatant, such as air, to pass therethroughwithout significant losses. The sleeve may comprise circular hoops ateither end thereof, as series of mutually circumferentially spaced andaxially extending longeron members, such as about 10 to 50 said longeronmembers, as well as one or more intermediate circumferential hoops spacein a series along the support sleeve. The longeron members may be spacedfrom one another roughly the same distance that the hoops are spacedfrom one another to form generally square shapes or spaces which may bereinforced by x-shaped diagonal members such that all of theperforations through the internal support sleeve are triangles. Thisstructure has been found to provide a lightweight form which isnoticeably strong for resisting substantially radially inward loadswhich may be placed thereon without producing significant flow lossesand also carries gravitational and inertial loads during flight. In thecase of an arrangement with radially outwardly travelling air, a similarsupport sleeve or bird cage could be provided radially outside thecoolant tubes.

It is possible to arrange one or more intermediate header tubes locatedpart of the way along the route of the small diameter tubes from theinlet heads thereof to the outlet headers thereof. Thus, the tubes mayconceptionally be thought of as “cut” part way along their length andwith each of the cut ends attached to the intermediate header tube. Aninternal intermediate supply tube may be inserted within theintermediate header tube to extend substantially all of the way alongits length, the intermediate supply tube having a series of outletapertures formed in a series therethrough a long its length. Duringoperation of the heat exchanger coolant may be fed into the heatexchanger not only at the inlet header tubes but also at the internalintermediate supply tubes such that further coolant may be added at theintermedial header tubes and different mass flow rates of coolant mayflow through different parts of the heat exchanger, allowing the singleheat exchanger construction to act as though it is a plurality ofdifferent heat exchangers but with roughly only the cost and complexityof building one. It will be appreciated that to add the further coolantat the intermediate header tubes, the pressure of the supply at theintermediate header tubes may be controlled to be similar or the same asthe pressure of the nearby coolant inside the small diameter tubes. Theuse of the internal intermediate supply tubes with the series of outletapertures formed in a series therethrough ensures that the uniform flowconditions can be achieved along the axial length of the heat exchanger.

The heat exchanger of the preferred embodiment to be described hereinincludes a frost control system and after an actual test carried out ona test heat exchanger in confidential conditions for the European SpaceAgency on behalf of the United Kingdom government, the European SpaceAgency confirm a successful demonstration of the frost control mechanismat laboratory scale. The tested heat exchanger included a total of over40 kilometres of the small diameter tubes at a weight of less than 50kilograms and the incoming airstream was cooled to minus 150° C. inunder 20 milliseconds. No frost blockage was noted during lowtemperature operation and the European Space Agency stated they are nowconfident that a ground engine demonstrating test may now be performed.

The heat exchanger thus may be provided with one or more dogleg zones ineach spiral section, each dogleg zone in including a short radiallyextending section. Thus, each spiral section is not fully spiral inshape but comprises a first substantially spiral portion then a shortradial portion which is followed by another substantially spiral portionand so on. This construction causes the provision of a substantiallyarcuate box shape between the doglegs of adjacent spiral sections.

Within the arcuate box spaces are located a series of one or tworadially spaced and circumferential staggered rows of catcher elements.Each catcher element may comprise a tube having an interior which can beconnected to a suction system for sucking on the contents of a pluralityof exterior pockets spaced along the capture element on the leading facethereof, the pockets being connected via through-apertures to theinterior of the tube. The capture element leading face pockets may becovered with 50-micron silica-coated mesh to form a porous front face tothe pocket. A wetting agent other than silica may be used in otherembodiments as may meshes of different sizes.

In this embodiment, a methanol, or other anti-freeze substance,injection system is located upstream of the capture elements and aswater condenses out of the flow it mixes with the methanol whichmaintains the water as a liquid rather than freezing and this mixture isseparated from the air flow by inertial separation upon contact with thewet mesh of the capture elements, then being sucked by vacuum via thepockets and through-apertures and carried away along the captureelements. When there are a plurality of said dogleg zones in each spiralsection, a further set of similar catcher elements may be employed infurther-resulting arcuate box spaces. In this case, in an example whenthe air flow is radially inward and is being cooled, for example byhelium in the narrow tubes, pure or relatively concentrated methanol maybe injected at or just upstream of the radially innermost arcuate boxsection and then at least partially caught in a mixture with water bythe respective catcher elements, and this more dilute mixture may thenbe recycled further radially outboard in the heat exchanger where thetemperature is higher and caught again. Thus, the methanol may beconsidered in this embodiment to run in overall radial counterflowrelative to the air which reduces the required methanol consumption toprevent freezing and blockage.

The methanol could be fully separated from the water after use but itmay alternatively be allowed to pass with the engine supply air to acombustion section of the engine where it may contribute to thrust.While the thrust control system is running, the methanol’s (combustionproduct) weight ejected backwards from the main engine rocket nozzlesmay in some embodiments add 2% to thrust. Also, the loss of themethanol’s weight from the vehicle may be desirable in order to enable ahigher vehicle velocity to be achieved in response to engine thrustlater on during flight.

The frost control system described herein can remove typically 99% ofthe water content from air.

The conditions in the heat exchanger may be carefully controlled suchthat operation when considered on a water-methanol solid-liquid phasediagram the environment in the vicinity of the coldest catcher elementsis in the region of about 80 mol% or about 88 wt% methanol as thetemperature approaches about minus 100° C.

The two above-mentioned radially spaced and circumferentially staggeredrows of catcher elements can be configured with the leading row elementscircumferentially about half way between the adjacent elements of thetrailing row. The leading capture elements may act as bluff bodies whichdeflect condensed fluid, which may have built up on the narrowcoolant-containing tubes, in the flow generally towards the captureelements in the trailing row. This means that about 95% of the fluidremoved by the two rows may be removed by the trailing row and only 5%by the leading row. Thus, in some embodiments, the leading row ofcapture elements may be replaced by a passive row of bluff bodyelements, which could be flat sheets with slots or slits opposite thecapture elements.

The heat exchanger may be provided with deflector-shaped foil shims inthe region of the short radially extending portions of the smalldiameter tubes in order to ensure that the liquid flow is directedtowards the capture elements and does not easily take a short cut acrossthe tubes in the regions of these radial sections. Also, the gapsbetween the tubes in the radially extending portions are preferablysealed.

Thus, it is anticipated that the frost control system may be used in thelow atmosphere to remove water content from the air flow such that icingup and blockage of the heat exchanger does not occur. As the vehicletravels up towards the top of troposphere and towards the stratosphere,for example at an altitude of about 10 kilometres, thereabouts orsomewhat higher, there is no longer enough water vapour present to causetroublesome icing and the frost control system can be switched off byshutting down methanol pumps and capture element suction pumps.

Even though the heat exchanger could cool the air down to itsliquification point if necessary near the air outlet from the heatexchanger, i.e. near the internal bird cage when the flow is radiallyinward, the frost control system is set up so that the great majority ofthe water is removed with methanol at a higher temperature further backin the heat exchanger. At very low temperatures, down below about minus50° C. and all of the way down to near minus 140° C. any remainingmethanol-water liquid content will, if it solidifies, turn directly tomass ice rather than the feathery frost that can be formed at highertemperatures, by direct sublimation from the vapour, and so causes lessof a blocking issue.

When a reusable vehicle in which the heat exchanger is used, such as aSKYLON vehicle or similar craft, is travelling back into the atmosphereat high speed, air inlet nacelles to the engine may be closed. Even withno air passing through the heat exchanger, helium may be cycled aroundthe small diameter tubes in order to prevent overheating of the heatexchanger and potentially also nearby components due to aerodynamicheating via the outside body of the engine upon atmospheric re-entry.

In other embodiments, fluids other than helium may be flowed alonginside the heat exchanger tubes, such as hydrogen. Instead of acting asa helium/air heat exchanger, the heat exchanger may act as ahydrogen/other fluid heat exchanger (for example). The heat exchangertubes are generally circular in cross-section in the preferredembodiment although other shapes could be used in other embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention may be carried out in various ways and onepreferred embodiment of a heat exchanger, an engine and an aircraft inaccordance with the invention will now be described by way of examplewith reference to the accompanying drawings, in which:

FIG. 1A is a side elevation of one preferred embodiment of an aircraftincorporating an engine with a heat exchanger in accordance with apreferred embodiment of the present invention;

FIG. 1B is a top plan view of the aircraft of FIG. 1A;

FIG. 1C is a rear elevation of the aircraft of FIG. 1A;

FIG. 2 is a schematic view of a prior art engine;

FIG. 3 is a schematic cycle diagram for the engine of FIG. 2 which hasbeen modified to include a heat exchanger in accordance with a preferredembodiment of the present invention;

FIG. 4A is an isometric view of a preferred embodiment of a heatexchanger in accordance with the invention as used as a modified heatexchanger in a modification of the engine of FIG. 2 with a cycle asillustrated in FIG. 3 ;

FIG. 4B is a detail view on area A of FIG. 4A;

FIG. 5A is a section on Y-Y in FIG. 5B of the heat exchanger;

FIG. 5B is a side elevation of the heat exchanger viewed in a radiallyinward direction;

FIG. 6 is an isometric view of a drum-shaped bird cage or perforatedsleeve support for the heat exchanger;

FIG. 7A is a detail view of detail A in FIG. 7E;

FIG. 7B is a detail view on detail B in FIG. 7E;

FIG. 7C is a detail view on detail C in FIG. 7F;

FIG. 7D is a detail view on detail D in FIG. 7F;

FIG. 7E is a schematic section through the spiral section of the heatexchanger shown in FIG. 7F as though looking up from below in FIG. 7F;

FIG. 7F is an isometric view of a spiral section of heat exchanger tubesof the heat exchanger;

FIG. 8A is a view similar to FIG. 7F but with a substantial proportionof the heat exchanger tubes of the spiral section removed for thepurposes of clarity so as to show positions of baffle stations along thecurved generally circumferential length of the heat exchanger section;

FIG. 8B is a detail view isometric on detail E in FIG. 8A;

FIG. 8C is a detail view isometric on detail F in FIG. 8A;

FIG. 9A is rear elevational view on the heat exchanger in the direction9A in FIG. 9B;

FIG. 9B is a cross-sectional view of the heat exchanger on the twoplanes represented by the line A-A in FIG. 9A;

FIG. 10A shows the support member of FIG. 6 with optional longeron shoesfitted to longeron elements of the support and with the components ofthe spiral section shown in FIG. 8A fitted in a spiralling fashiontherearound;

FIG. 10B shows a detail isometric view on detail A in FIG. 10A;

FIG. 11A is an end view of the support of FIG. 6 with all 21 spiralsections fitted but with the capture elements and a methanol injectionring omitted for the purposes of clarity;

FIG. 11B shows an elevational detail view on detail A in FIG. 11A;

FIG. 12A shows a front elevational view of the methanol injectorassembly of the heat exchanger;

FIG. 12B shows a section on the plane A-A in FIG. 12A;

FIG. 12C is a detail view on detail B in FIG. 12B;

FIG. 12D is a detail view on detail C in FIG. 12B;

FIG. 12E is a partly shortened cross-sectional view on the plane D-D inFIG. 12G showing one of the injector tube assemblies of the injectorassembly;

FIG. 12F is a detail view on detail E of FIG. 12E;

FIG. 12G is an elevational view along the direction 12G in FIG. 12E ofthe injector tube assembly;

FIG. 12H is an isometric view of the injector assembly of FIG. 12A;

FIG. 13A is an isometric view of part of an outer capture assembly forremoving liquid from the heat exchanger in the frost control system;

FIG. 13B is a view in isometric of part of the components shown in FIG.13A;

FIG. 13C is an end view of the components shown in FIG. 13A;

FIG. 13D is a section on the plane C-C in FIG. 13C;

FIG. 13E is a view similar to FIG. 13C but with a capture manifold plateof the capture assemble removed;

FIG. 13F is a detail view on detail D in FIG. 13E;

FIG. 13G is an elevational view in a circumferential direction (aroundthe drum center axis of the heat exchanger) of the parts shown in FIG.13A;

FIG. 13H is a section on the plane A-A in FIG. 13G;

FIG. 13I is a detail view on the detail B in FIG. 13H;

FIG. 14A is an elevational view in a circumferential direction of acapture tube of the capture assembly as hydroformed;

FIG. 14B shows the cross-sectional profile of the hydroformed capturetube of FIG. 14A at a circular end spigot thereof;

FIG. 14C shows the profile section of the capture tube of FIG. 14A at araised point of the profile shown in FIG. 14A, at one end of each of twoadjacent liquid capture pockets;

FIG. 14D shows the profile of the tube mid-way between two such pocketends;

FIG. 14E shows a perspective view of the tube of FIG. 14A;

FIG. 14F shows a sectioned perspective view of the tube of FIG. 14A witha silica-coated mesh wrapped tightly therearound;

FIG. 15 is a schematic view of a modified version of the spiral sectionsincluding an intermediate header;

FIG. 16 is a schematic view showing the heat exchanger and intermediateheader fluid flow path;

FIG. 17 shows a schematic view of part of the spiral section viewed inthe direction 17 in FIG. 15 ;

FIG. 18 shows schematically a modified injection system in whichmethanol (or other antifreeze) is recycled and injected more than onceinto the air flow;

FIG. 19A shows a shim plate used with catcher elements of the captureassemblies;

FIG. 19B shows the shim plate of FIG. 19A positioned relative to thecatcher elements;

FIG. 19C is a partial end view of the heat exchanger;

FIG. 19D is a detail view on detail E of FIG. 19C;

FIG. 20A is a front view of the heat exchanger with circular catcherring manifolds and S-shaped connection hoses thereof removed for thepurposes of clarity;

FIG. 20B is a detail view on detail A of FIG. 20A;

FIG. 21A is a schematic view of the heat exchanger placed around anoutlet duct together with two passive units, the outlet duct leading ina longitudinal direction towards an air compressor of the engine; and

FIG. 21B is a detail view on detail B of FIG. 21A.

DETAILED DESCRIPTION

As shown in FIGS. 1A, 1B and 1C, an aircraft 10 with a retractableundercarriage 12, 14, 16 has a fuselage 18 with fuel and oxidant stores20, 22 and payload region 24. A moving tail fin arrangement 26 and allmoving canard arrangement 28 are attached to the fuselage 18. Main wings34 with elevons 36 are attached to either side of the fuselage 18 andeach wing 34 has an engine module 38 attached to a wingtip 40 thereof.As shown in FIGS. 1C and 2 , a rear of each engine module 38 is providedwith four rocket nozzles 40 surrounded by various bypass burners 42.

As shown in FIG. 2 , the prior art engine module 38 includes an airinlet 43, heat exchanger 44 in four parts, a turbo compressor 46 andcycle conduits 48. In an air breathing mode of the engine module 38inside the Earth’s atmosphere, part of the incoming air passing throughthe air inlet 43 passes through the heat exchanger 44 to the turbocompressor 46 and part is bypassed along bypass duct 50 to the bypassburners 42.

In the preferred embodiment, the prior art heat exchanger 44 is replacedwith the heat exchanger or pre-cooler 52 or a plurality of said heatexchangers 52 operable in parallel.

FIG. 3 shows a schematic view of the cycle for the modified enginemodule 38, which has been simplified for the purposes of clarity to showonly one rocket nozzle 40 instead of four.

Thus, as shown in FIG. 3 , in the air breathing mode, air enters theintake 43 and passes either to the heat exchanger 52 or via the bypassduct 50 to the bypass burners 42. The air passing through the heatexchanger 52 is then compressed in a compressor 54 of the turbocompressor 46 before passing through valve 56 to rocket nozzle 40 andpartly also to the pre-burner 58 before passing through heat exchanger60 before passing with uncombusted hydrogen in pre-burner exhaustproducts for further combustion at the rocket 40.

A liquid hydrogen pump 62 driven by a turbine 64 drives hydrogen througha heat exchanger 66 and the turbine 64 through a turbine 68 of a heliumcirculator 70 to the pre-burner 58 for partial pre-burner combustion,although some of the liquid hydrogen may be bypassed by valve 72 alongthe conduit 74 for combustion in the bypass burners 42.

The helium circulator 70 includes compressor 76 which drives gaseoushelium through the heat exchanger 52 in counter-flow heat exchange withthe air passing in the opposite direction (considering radial componentsof the paths of the air and helium), the helium then passing throughheat exchanger 60 before travelling through helium turbine 78 beforebeing cooled by the hydrogen in heat exchanger 66 and then passing backto the helium compressor 76. In this air breathing mode, the aircraft 10is able to take off horizontally from stationary on the ground 80 (FIG.1A).

Once the aircraft 10 is travelling at a significant speed ofapproximately Mach 5, it may switch from the air breathing mode into afull rocket mode. In the full rocket mode, the air inlet 43 is closed;the path of hydrogen through the cycle conduit 48 is similar to that inthe air breathing mode although no hydrogen is diverted by the valve 72to the bypass burner 42. The turbo compressor 46 is inactive. In thehelium circuit, the gaseous helium now flows from the helium compressor76 through heat exchanger 52 and heat exchanger 60 but then to turbine82 before returning to the heat exchanger 66 and then to the heliumcompressor 76. The helium turbine 82 drives liquid oxygen pump 84 whichdirects oxygen towards the rocket nozzle 40 as well as partly via thepre-burner 58 and then as a pre-burner exhaust product together withunburnt hydrogen to the rocket nozzle 40 for combustion therein. Thevalve 56 is closed in the full rocket mode.

In the full rocket mode, the aircraft 10 may accelerate up through highMach numbers and into orbit.

As shown in FIG. 6 , the heat exchanger 52 has a support in the form ofa central bird cage or generally cylindrical perforated drum 84. Thedrum 84 has two end support rings 86 spaced apart from one another andthree intermediate support rings 88 which are spaced apart in an evenseries between the end support rings 88. A series of 21 longeron members90 extend along between the two end support rings 86 and are supportedby all five of the support rings 86, 88. The longeron members 90comprise substantially flat radially aligned and thin plates. Thelongeron members 90 are attached by threaded bobbin members 92 to thetwo end support rings 86 and have a series of three slots 94 nearradially inner edges 96 thereof. The slots 94 extend approximately onequarter to three quarters of the radial extent along each longeronmember 90 and enabling supporting engagement between the longeronmembers 90 and the intermediate support rings 88. The intermediatesupport rings 88 also have slots, which correspond, to enable theengagement shown in FIG. 6 .

The support drum 84 also includes an internal stiffener tube 98 whichcomprises a perforated tubular element having longitudinal membersengaging along the full length of each of the longeron members 90,circumferentially extending members 102 extending along the fullcircumferential extent and engaging each of the support rings 86, 88, aswell as X-shaped bracing members 104 located adjacent to generallysquare spaces 106 formed between the various longeron members 90 andsupport rings 86, 88. The stiffener tube 98 therefore forms a very stiffperforated lattice within the drum 84 which is designed to carry shearloads. The drum is capable of accepting a high radially inward load andthe four triangles formed in the region of each X-shaped bracing member104 enable substantial airflow to pass radially through the perforateddrum 84 without a significant pressure drop.

As shown in FIG. 10A, 21 spiral conduit sections, only one of which isshown and which is only partly shown in this Figure, may be securedaround the perforated drum with an inlet header 106 of each modularspiral section 108 secured to the support drum 84, the spiral section108 spiralling outwardly radially away from the central axis of the drum84 as it extends circumferentially substantially 360° around the supportdrum 84 to an outlet header tube 110. Each spiral section 108 may bemodified in other embodiments to extend a greater or less angle around.As can be seen in FIG. 10A, the modular spiral section 108 includesfirst 112′ and second 114′ dogleg sections containing short radiallyextending sections of heat exchanger tubing as will be described below.In other embodiments more than two such dogleg sections may be used,such as three, four or five in each spiral section 108.

FIG. 10B shows how the inlet header tube 106 includes a series of fivemounting flanges 112 (only some of which are shown in FIG. 10B) whichhave apertures (not shown) engaged by a locking rod 114 to lock theinlet header tube 106 in position to each of the support rings 86, 88.As can be seen in FIG. 10B, an optional longeron shoe 116′ covers theradially outer edge of each longeron member 90 to protect the spiralsections 108 which may engage therewith. The longeron shoes 116′ are notused in other embodiments. FIG. 8A also shows the location of bafflestations 116 which are regularly spaced along the spiral sections 108.

FIG. 8B shows that the outlet header 110 (and the inlet header 106 issimilar) has within it a series of 800 apertures 118 configured toaccept 800 corresponding helium heat exchange tubes 120 only three ofwhich are shown in FIG. 8B. Other embodiments may employ fewer or,indeed, more such tubes 120. The helium tubes 120 are brazed into theapertures 118. To prepare the helium tubes 120 for brazing, preferablythe tubes are scanned for defects, wall thickness is measured (OD), apressurization test is conducted, and the tubes are optionallyelectrochemically milled, washed, dried, and then cut and formed toshape. The brazing is preferably carried out under vacuum.

The helium tubes 120 are arranged in 200 rows spaced along the axialdirection of the headers 106, 110 and four rows radially. The heliumtubes 120 extend all of the way along from each inlet header 106 to eachoutlet header 110. Since there are 21 spiral sections 108 and each tube120 is approximately 2 to 3 meters long, the heat exchanger 52 containsapproximately 40 kilometres of the tubes 120. The tubes 120 areapproximately 1 millimetre in diameter or somewhat more and have a wallthickness of about 20 to 40 microns.

FIG. 8C shows how the tubes 120 pass the doglegs 112′, 114′ with shortradial portions 122 and J-shaped foils or joggles 124 located eitherside of the doglegs 112′, 114′ to direct flow away from the radialportions 122. This is also shown in FIG. 7B. As can be seen in FIG. 7A,at the baffle stations 116, race track section baffle elements 125 arebrazed to the inner side of each of the four rows of helium tubes 120 inany given spiral section 108 and a flat shim plate 126 is based to theouter side of the radially outer tubes 120 in the four rows. The baffleelements 125 are made by flattening tube the same as the helium tubes120. The baffle elements and shim plates 126 extend axially the fulllength of all of the 200 rows of tubes 120 in the axial direction. Asshown in FIG. 11B, the baffle stations 116 of the 21 spiral sections 108are substantially aligned with one another wherever there is a longeronmember 90 so as to be orthogonal to the matrix tubes 120, althoughoffset slightly angularly from the true radial direction R (see FIG.11B) from the central axis 128 of the heat exchanger 52 (see FIG. 11A).Therefore, the shoe 116′ on the longeron member 90 engages the bottombaffle element 125 of a first spiral section 108 and radial force can betransmitted through the baffle station 116 to the shim plate 126 whichengages the bottom of another radially inner baffle element of the nextinter-nested spiral section. After the 11^(th) spiral section 108, aradially extending I-beam 130 may transmit the substantially radial loadto the next spiral section 108. After a further seven sets of baffleelements 125 and shims 126 of a further seven spiral sections 108, thereis a further substantially radially extending I-beam 130 fortransmitting radial load and there are then a further three sections 108that are passed in the radial direction until the spiral sections 108,all twenty-one of them, have been fully counted. This configuration isillustrative only and may differ in other embodiments.

When the heat exchanger is operational, there is a substantial inwardflow radially of air past all of the tubes 120 placing a substantialradially inward aerodynamic load on them. This load is countered by thesubstantially aligned shim plates 126, baffle elements 125, I-beams 130and longeron members 90 which are aligned substantially in the radialdirection. Accordingly, despite the very substantial aerodynamic loads,the tubes 120 may be securely supported.

In some cases, particularly at high Mach numbers, the air inlettemperature to the heat exchanger 52 at the radially outermost side inparticular may be substantial, for example over 800 or even 1000° C. Thetemperature variation may cause a significant thermal change to thetubes 120 which, in particular, may grow in length with increasingtemperature. Therefore, although the inlet header tube 106 is fixed inposition to the perforated support drum 84, the outlet headers 110 maymove as the tubes 120 grow in length. The shim plates 126 of each spiralsection 108 may therefore slide relative to the adjacent baffle elements125 to enable sliding substantially circumferential motion of the spiralsections 108 relative to one another. With lengthening of the tubes 120due to increased temperature, the line of thrust of the baffle stations116 through the baffle elements 125, shim plates 126 and I-beams 130 mayrotate to be more in line with the truly radial direction of R from thecentre axis 152 of the exchanger 52. The line of the baffle elements 125is maintained substantially orthogonal to the tubes 120. Therefore,thermal expansion and contraction of the tubes in the circumferential(lengthwise) section of the tubes 120 may be allowed for. Naturally, thetubes 120 and other components may expand in the radial direction asthey expand and contract with temperature and allowance for this is alsoprovided.

As can be seen in FIG. 7D, each inlet header tube 106 is fitted withinlet header fittings 140 at either end thereof and the outlet headertubes 110 are fitted with outlet header fittings 142 at the respectivetwo ends thereof. As shown in FIGS. 4A and 5B, the inlet header fittings140 at one end of the inlet headers 106 are fluidly connected byflexible hoses 144 to the inlet manifold 146 for the helium flow, andoutlet header fittings 142 at the same end thereof are fluidly connectedby flexible hoses 148 to helium outlet ring manifold 150 for the helium.

The inlet header fittings 140 at the other end of the header tubes 106may be blocked off or may be fluidly connected via a ring manifold tothe adjacent header fitting 140. The same is so for the outlet headerfittings 142 at the other end of the outlet header tubes 110.

As can be seen for example in FIGS. 11A and 11B, generally rectangular(but arcuate) pockets (or box sections) 160 are created extendingaxially all of the way along the heat exchanger 52 between the tubes 120of adjacent spiral sections 108 in the regions of I-beams 130 and therespective doglegs 112′, 114′. These generally rectangular but arcuatepockets 160 contain capture elements 162 of a frost control system ofthe heat exchanger 52 which will now be described.

As shown in FIGS. 4A and 12A, a methanol supply tube 170 feeds methanolto an annular gallery 172 of a methanol injection ring 174. The parts176 in the gallery 172 are sections through tubes 214 where these enterthe gallery 172.The methanol injection ring has a series of 180 injectortubes assemblies 182 (FIG. 12E) (this arrangement could differ in otherembodiments) located in a series spaced circumferentially around theheat exchanger 52, each injector tube assembly 182 including an injectortube 184 extending axially between annular manifold 173 forming theannular gallery 172 and a further support ring 175 into which taperedends 190 of end plugs 192 are fixed. Each of the injector tubes 184includes a series of 22 injection holes 194 (one of which is shown inFIG. 12F) spaced therealong in a series along the tube 184, the diameterof each of the holes 194 being 0.2 mm. The end 196 of each tube oppositethe tapered end 190 is secured to an injector fitting 198 having anon-circular flange 200 with a flat 202 for rotationally aligning thetube 184 by matching of the flat 202 with a corresponding formation in asupport ring 177 attached to the ring 173. A circular seal 204 isprovided for sealing in an annular recess 206 of the fitting 198.

When a methanol pump 210 (FIG. 3 ) is operated to pump methanol along aconduit 212 which is connected to the methanol supply tube 170, themethanol is forced through the gallery 172 and through supply channels214 of the ring 173 and interior channels 216 of the fittings 198 topump methanol into the interior of the tubes 184 and then out throughthe injection holes 194. Accordingly, methanol is injected into airflowjust about to enter into the volume defined by the spiral sections 108of the tubes 120.

The methanol is able to prevent the formation of ice in the heatexchanger 52 which would block the airflow through the same. Themethanol lowers the freezing temperature of water droplets condensed outwithin the heat exchanger to do this and a substantial proportion of themethanol and water are together removed from the airflow by catcherelements as will now be described.

Each outer one of the two pockets 160 shown in FIG. 11B has ninemutually spaced catcher elements located therein and each inner one ofthe pockets 160 has seven catcher elements 162 located therein. Withreference to FIGS. 13A to 14D of the drawings, the catcher elements 162will now be described. These Figures show one outer catcher assembly 240having nine catcher elements. The inner catcher assemblies are similarapart from the number of catcher elements (since they only have seven).As shown in FIGS. 13A and 13H, each catcher assembly 240 has an outerrow 242 of four catcher elements 162 and an inner row 244 of fivecatcher elements 162. Again, the numbers of catcher elements and thenumbers of doglegs and rows (radially) of pockets may differ in otherembodiments. Each catcher element 162 comprises a hydro-formed tube 246with a varying cross-section along the length thereof as shown in FIGS.14A to 14D. In particular, the tube 246 is circular in section atrespective ends 248, 250 thereof and has eight pocket depressions 252formed therein between peaks 254 where the cross-section of the tube 246is as shown in FIG. 14C, the cross-section a mid-point 256 between thepeaks 254 being as shown in FIG. 14D in which there are two outwardlyconcave portions 258. As shown in FIG. 13I, the tubes 246 are coveredwith a stainless steel 50 micron filter mesh 258 (other meshes may beused in other embodiments) which is coated with a wetting agent such assilica. Each mesh 258 is generally cylindrical (it may vary in otherembodiments) and forms a pair of cavities 260, 262 at each of the pocketdepressions 252, such that there are sixteen cavities 260, 262 in totalper catcher tube 246. Scavenge holes 264 are positioned through the wallof the tube 246 in each cavity 260, 262 - this number may differ inother embodiments. The catcher assembly 240 includes a control plate 270and one end 248 of each catcher tube 246 is fitted to a non-rotationalfitting 272 such that all nine catcher element tubes 246 communicatewith the interior of a catcher suction manifold assembly 274 having asuction port 276 leading, via piping 278 (FIG. 3 ), to suction source280. The catcher elements 162 are capable of operating upside down andalso when used in any axially or otherwise accelerating flying vehicle.

As shown in FIGS. 13A and 13D, the distal ends 282 of the catcherelements 246 are securely closed by end plugs 284.

It will be seen that the catcher control plates 270 includes circularapertures 290 therethrough. The outlet header tubes 110 of the heatexchanger 52 pass through these apertures 290. It will also be seen thatthe catcher plate 270 includes nine extra apertures 292. The reason forthis is that the adjacent catcher assembly 240 spaced onecircumferentially around the heat exchanger 52 is arranged with themanifold 272 and end plugs 284 at opposite ends. Therefore, theapertures 292 serve to engage around the circular ends 250 of thecatcher elements 162 of the adjacent catcher assembly 240 so that all ofthe catcher tubes 246 are supported at both ends. With a vacuum appliedat the suction port 276, there is suction at the scavenge holes 266.With methanol and water in liquid form in the region of the catcherelement 162, when the liquid touches the silica coated mesh 258, itbecomes wetted onto the mesh 258 and is sucked through the mesh (thecavities 262 operating at a low pressure due to the small mesh pores),into the cavities 262, 260/pockets 252, then through the scavenge holes266 and along inside the catcher tubes 246 to the respective manifold274 and suction port 276. The scavenge holes 266 control the air flowsucked through with the liquid to a low level. In this way, asubstantial proportion of the water vapour in the incoming air may beremoved from the flow such that the heat exchanger 52 does not blockwith ice. Whereas the mesh 258 is shown with a circular section for thepurposes of clarity in FIG. 13I, as shown in FIG. 14F, the mesh in factstretches out to a flatter configuration over the cavities262/260/pockets 252. As shown in FIG. 14E the peaks (or lands) 254 areconfigured generally flat. The lands 254 engage the mesh 258 so as toseparate the pockets from one another. Thus, if one pocket should loseits integrity, for example if debris is ingested into the heatexchanger, the other pockets 252 will remain operational.

As shown in FIG. 4B, the outer catcher suction manifold assemblies 274are connected by flexible S-shaped vacuum tubes 300 — the S-shape allowsfor manufacturing differences and for thermal expansion but need not beemployed in other embodiments — to annular frost control catcher ringmanifold 302 and the inner catcher element manifold plates 304(corresponding to the manifold plates 274 but for only seven catcherelements) are connected by similar S-shaped flexible hoses 306 to frostcontrol catcher ring manifold 308. The ring 308 leads to a vacuum outletconduit 309 and ring 306 to a vacuum outlet conduit 307 both leading viathe piping 278 to vacuum source 280.

Since there are similar vacuum manifold plates 272, 304 at the oppositeaxial end of the heat exchanger, a similar arrangement of S-shapedflexible hoses 300, 306 and frost control catcher ring manifolds is alsoprovided at that end, as shown in FIG. 5B with similar referencenumerals denoting similar features.

It will be noted from FIG. 13H that the spacing between the catcherelements 162 along the length of each of the rows 242, 244 isapproximately one third of the diameter of the catcher elements 162. Itwill also be noted that the distance between the catcher elements 162 inthe row 242 and the catcher elements in the row 244 is approximately thesame or slightly less. When liquid droplets 400 approach the outer row242 they may travel and turn approximately as shown by arrows 402.Droplets flow through the matrix of tubes 120 and whilst growing on thetubes are focused laterally by the airflow accelerating into the gapsbetween the catcher elements 162 of the outer row 242. Therefore, thedroplets 400 tend to be diverted by the catcher elements 162 in thefirst row 242 to be travelling almost straight towards the catcherelements 162 in the next row 244. In practice, this means that thecatcher elements 162 in the row 242 may act as bluff bodies and about 5%of the water extracted by the catcher assembly 240 may be extracted inthe front row 242 (in the sense of airflow direction) and 95% in thenext row 244. In other embodiments, the front row catcher elements 162of the row 242 may be replaced with solid bodies with no mesh or suctionfunction.

With the heat exchanger 52 in operation, the temperature at the innercatcher elements and/or outer ones may be monitored by a temperaturesensor 350 which may send data to a controller 352 (FIG. 3 ) which maycontrol a valve such as the valve 354 with a diverter part 356 foraltering the helium flow through the heat exchanger 52. In this way orin a similar way, the temperature at the catcher elements 162 may becontrolled. The water and methanol removed from the airflow may be addedback into the airflow approaching the rocket nozzle 40 and may in someembodiments add 2% to thrust. The loss of the methanol’s weight from thevehicle may be desirable also in order to enable a higher vehiclevelocity to be achieved in response to engine thrust later on duringflight. The frost control system described herein can typically remove99% of the water content from air. The control provided by thecontroller 352 just described may be such that on a water-methanolsolid-liquid phase diagram the environment in the vicinity of thecoldest catcher elements 162 is in the region of about 65 mole % orabout 82 wt. % methanol as the temperature approaches about -100° C.Even though the heat exchanger could cool the air down to itsliquification point if necessary near the air outlet from the heatexchanger, the frost control system is set up so that the great majorityof the water is removed with methanol at a higher temperature furtherback in the heat exchanger. At very low temperatures down below about-50° C. and all of the way down to near -140° C. any remainingmethanol/water liquid content will, if it solidifies, turn directly tomass ice rather than the feathery frost that can be formed at highertemperatures, by direct sublimation from the vapour, and so causes lessof a blocking issue.

As shown in FIG. 15 , the spiral sections 108 may be modified toincorporate an intermediate header 440. The intermediate header 440 mayhave two sets of apertures, into one set of which all of the tubes 120arriving from the inlet header 106 may be fixed by brazing and intowhich other set all of the tubes 120 leading to the outlet header 110may be so fixed. The intermediate header 440 may have an outer tube 442thus into which the tubes 120 communicate. The inlet header 440 mayinclude an interior tube 444 having a series of injector apertures 446located in a series at spaced locations therealong for injecting heliuminto the intermediate header 440. Therefore, the tubes 120 downstream ofthe intermediate header 440 may carry more mass flow rate of helium thanthe tubes 120 upstream. This may be extremely useful in cycle design tobe able to vary heat exchange characteristics substantially, for exampleto prevent exceeding allowable metal temperatures at high flight Mach,and in what is only one heat exchanger 52 essentially provides a systemwhich may act like two different heat exchangers with different flows ofcoolant, helium or another coolant, flowing in them. This may be seenschematically in FIG. 16 where air is seen flowing along one path 450,and inlet header 106 may conceptually be thought of at an inlet point inthe heat exchanger 52, intermediate header 440 at an intermediate pointand an outlet header 110 at an outlet point. A control valve 452 isschematically shown for controlling the flow of coolant into theintermediate header 440.

As shown in FIGS. 19A to 19B, a shim plate 500 is located in each pocket160 located radially outside the catcher elements 162 of the rows242,244. FIG. 19A shows the shim plate 500 for the outer pockets 160,the inner pockets with seven catcher elements 162 having similar shimplates 500 (although the number of longitudinal slots 512,514,516 may bechanged e.g. reduced). Each shim plate has a first side wall 502, a topwall 504 and a second side wall 506. Each side wall 502,506 comprises adownwardly slanted portion 508 joined to the top wall 504, thedownwardly slanted portion 508 being connected to a lower generallyradially extending portion 510 of the side wall 502. The top wall 504defines generally all of the way therealong three longitudinallyextending slots 512,514,516, the slots 512,514,516 being interrupted bya series of small cross-connectors 518. The three slots 512,514,516 arealigned along respective radial paths with the three middle-most catcherelements 126 of the second row 244 of catcher elements 126. Therefore,as shown by the five air flow lines 520 shown in FIG. 19D, the slots512,514,516 in the shim plates 500 tend to assist in directing the flowonto the catcher elements 126 in the second row 244. The arrangement maybe modified by omitting the first row 242 of catcher elements 126 andpotentially by placing the top wall 504 of each shim plate 500 nearer tothe remaining “second” row 244 with the slots 512,514,516 still beingsubstantially aligned with the catcher elements 126 thereof. In someembodiments, the shim plates may have one slot (or slit) per catcherelement 126 in this row. There are not necessarily three slots. Therecould be, for example five.

The shim plates 500 are optional. They locally increase air flowvelocity so that aerodynamic forces are dominant over gravity. Gravitymay tend to cause drops to move diagonally between catcher elementswithout hitting them and being caught. The shim plates 500 thus assistin the production of aerodynamic loads on droplets of water/anti-freezewhich tend to direct them onto the catcher elements 126, 244. Otherstructures than the shim plates 500 be used in other embodiments for asimilar purpose.

As shown in FIG. 20A, and FIG. 9B, the heat exchanger is provided with afront bulkhead 530 and a corresponding rear bulkhead 532, thesebulkheads being essentially mirror images of one another. The bulkheads530, 532 are secured with attachments to allow for movement due tothermal expansion. As shown in FIG. 20A, the front bulkhead 520 has aninner ring 534 sitting around and secured to the support drum 84. Theinner ring 534 is connected by a series of generally radially extendingspokes 536 with an outer ring 538 of the bulkhead 530. Outer ends 540 ofthe spokes 536 are connected to the methanol injection ring 174. Asshown in FIG. 20B, an outer header retainer spring 542 is spring-locatedto the ring 538 of the bulkhead 530 and to a tab washer 544 for theheader tube 110 attached to each catcher assembly control plate 270. Aspring 542 applies a light radial clamping load to the matrix of tubes120 whilst allowing thermal expansions.

Spokes 536 are slightly spiral in shape in this embodiment to provide aclearance but could be truly radial or have other configurations inother embodiments.

FIG. 18 shows a modification to the heat exchanger to incorporaterecycling of the methanol or other antifreeze used to prevent blockingof the heat exchanger due to frost or ice formation. The air flow flowsthrough the heat exchanger annularly inwardly, as before, shownschematically in the direction of the airflow arrows A,B with the airflow being cooled by the helium tubes 120 (not shown in FIG. 18 for thepurposes of clarity) and make it not shown in FIG. 18 (for the purposesof clarity). Methanol (or other antifreeze) is fed from a source/pump550 along a conduit 552 to a first injector manifold 554 located at arelatively cold downstream location in the air flow in the heatexchanger 52. The methanol is then collected or a significant portion ofit is collected with water in the air flow at a first downstream captureor removal arrangement 556. This captured methanol, diluted with thewater is then recycled by a pump 558 along a conduit 560 to a moreupstream methanol/water injection manifold 562 and this mixture is then(at least partly) captured along with more water from the air flow at afurther capture or removal arrangement 564. This methanol (together withwater) is then pumped by a further pump 566 along a further conduit 568with the methanol further diluted to an upstream methanol/water injectormanifold 570 where it is injected into the air flow. This furtherdiluted methanol (diluted with water) is then collected or substantiallyall collected at an upstream catcher or removal arrangement 572 fromwhere it is led away to an exit 574, which may lead to a combustion orthrust producing section of the engine in order to be ejected from theengine to supply additional thrust. This recycling of the methanol inwhich it is re-injected each time at a location further upstream (andthus can conceptually be considered in counter flow to the air flow eventhough as shown by schematic arrows 577 the methanol flows along withthe air while in the air flow) enables consumption of methanol or otherantifreeze to be optimised to a minimum.

It is envisaged that in some embodiments the methanol and water may belead away from the exit 574 to a methanol separator, such as adistillation system, for re-concentrating the methanol for re-use so asto reduce overall methanol consumption and the weight of methanol to becarried.

Instead of the arrangement shown in FIG. 18 it would be possible to havetwo or more catcher sections (like catcher arrangement 572) in series(one after the other along the air flow path) after each injectionmanifold (like 562) and before the next ejection manifold.

As shown in FIG. 21A the heat exchanger 52 (or pre-cooler) may beassembled in a test rig 580 together with a front passive heat exchangersimulator 582 and a rear passive heat exchanger simulator 584. Thesimulators 582,584 have similar air flow characteristics to the heatexchanger 52. The air flow simulators 582,584 and heat exchanger 52 arearranged annularly around an outlet duct 586 with a centre line or axis588. In practice for a flight-ready arrangement of three (or anothermultiple of) heat exchangers 52 next to one another in a similarconfiguration, the front and rear passive air flow simulators 582,584may be replaced by additional heat exchangers 52 which may besubstantially identical to the middle heat exchanger 52. These threeheat exchangers 52 may thus accept incoming air flows 590 from duct 592leading from inlet 43 and the outlet duct 586 may lead to the aircompressor 54 of the turbo compressor 46 shown in FIG. 3 .

The airflow simulators 582,584 and heat exchanger 52 are each radiallyinwardly bounded by a series 594,596,598 of overlapping guide vanes 600,each guide vane being an annular or ring-like element co-axial with thecentral axis 588. Each guide vane has a longitudinal extent along theaxis 588 and in cross-section as shown in FIG. 21B has a curvedgenerally radiused leading portion 602 extending approximately 20% ofthe longitudinal extent of the guide vane and a trailing portion 604extending the remaining approximately 80% of the longitudinal extent ofthe guide vane 600 which is substantially conical - although FIG. 21Bshows the leading edge portion 614 to be several flattened portions itis in fact preferably smoothly curved. Due to the configuration of thevanes in which they are curved and inter-nested, and in which an exitarea 606 between adjacent guide vanes 600 is considerably smaller thanan entrance area 608 between or near leading edges 610 thereof (bearingin mind both a smaller slot length transverse to flow as shown in crosssection and a smaller circumference at the exit area 606 too), the flowis turned and accelerated through the guide vane 600. Each guide vane600 is substantially the same width all the way along from its leadingedge 610 to a trailing edge 612 thereof but this could be changed inother embodiments. The leading edge 610 (or leading edge portion 614) ofeach guide vane 600 is angled at approximately 10 degrees to radial,i.e. the angle A in FIG. 21B. The trailing edge 612 (or trailing edgeportion 616) of the guide vane 600 is angled at approximately 10 degreesto the longitudinal axis 588 of the duct 586, i.e. the angle B in FIG.21B.

The guide vanes 600 serve to locally turn and accelerate the air flow upto the air velocity generally in the outlet duct 586 such that upstreamvelocity distribution, i.e. upstream of the front and rear passive airflow simulators 582,584 and the heat exchanger 52, is forced to becomemore uniform such that the same or substantially the same air mass flowrate will flow through each even though they are different distancesalong the duct 586.

Although it was originally assumed that a centre body inserted into theoutlet duct 586 would eradicate the problem of static pressuredistribution along the outlet duct reducing in the direction towards theengine, such a centre body unexpectedly did not when tested by thepresent applicants have the desired effect and forced even more of theflow to be drawn through the rear of the installation, the reason forthis (the present applicants have worked out) being that the airentering the outlet duct enters in the radial direction but subsequentlyfollows a curved path in order that it turns through 90 degrees to exitthe outlet duct and whenever the fluid follows a curved path there is apressure gradient perpendicular to the flow and the flow entering theoutlet duct towards the rear of the installation (nearer duct exit 589)was found to follow a tighter radius of curvature than the air enteringthe duct from nearer the front 591 thereof, with the tighter radius ofcurvature and high velocity towards the rear causing larger pressuregradients and resulting in a higher pressure region underneath the frontpassive airflow simulator 582 compared to the rear passive airflowsimulator 584, thus causing higher velocities drawn across the rearpassive air flow simulator 584 than the front passive airflow simulator582.

The turning vanes 600 alleviate this problem locally at the exit of thedrum-like air flow simulators 582,584 and heat exchanger 52. Althoughbetween neighbouring vanes 600 there will still be a pressure gradientin the axial direction, this is now constrained between boundaries ofvane pairs. Hence by splitting the flow into a sufficient number ofturning segments, the larger outlet duct pressure gradient can beremoved or at least reduced. Not only are more even mass flow ratesdrawn through the three drums 582,584,52 but the streamlines across theheat exchanger 52 become almost radial (reducing a tendency without thevanes for more flow to pass through the heat exchanger 52 at one axialposition than another), thereby helping to ensure a more uniform flowfield through the heat exchanger 52 for the purposes of heat transfer.

With the turning vanes 600 installed, the pressure ratio, i.e. the ratioof pressure in the duct 586 in the region of the front airflow simulator586 to the pressure in the region of the rear simulator 584 was seen toimprove from a ratio of 72% without the guide vanes 600 to 89% with theguide vanes installed as shown in FIG. 21A.

The vanes 600 are thus shown to offer a solution to re-distributing themass flow through a heat exchanger assembly having a longitudinal extentand leading to an axially-flowing duct and/or arrangements with multipleheat exchanger modules like the module 52 together with similar modulesreplacing the passive air flow simulators 582,584. The vanes 600 providemore uniform radial velocity distributions through the heat exchanger52.

The blade outlet angles (B) may be varied along the axial length of theinstallation to increase uniformity of flow yet further and it isenvisaged that a centre body 603 may be added as well such that acombined turning vane and centre body geometry can be utilised toprovide a highly uniform flow distribution with minimal total pressureloss. With the outlet duct 586 generally cylindrical, the centre body603 may be parabolic in cross-section, as schematically shown, in orderto provide generally linear area increase per unit length (due to the 3Dannular shape), enabling mass flux to remain substantially constant.

As shown in FIG. 21A, as well as inner guide vanes 600, each heatexchanger 52 may also be provided with a series of outer guide vanes 601extending fully along the axial length thereof, or substantially so.Only three such outer vanes 601 are shown in FIG. 21A for the purposesof clarity. The outer vanes 601 are preferably each slotted as shown inFIG. 21A since pressure increases and the flow velocity slows as flowpasses the vanes 601 and the slotting stops flow stall. Slotting is notneeded on the inner vanes 606 since pressure decreases and flowaccelerates across them. With the flow reversed outwardly radial inother embodiments, the inner vanes may be slotted. In some embodiments,either the inner 600 or the outer 601 vanes may be omitted.

As shown, for example, in FIG. 13B, the catcher plates 270 have pegs 700which protrude into the catcher pockets in the matrix of tubes 120 whichallows them to follow the catcher pockets as the matrix moves underthermal and pressure displacements. It will be appreciated that thecatch plates 270 overlap so as to prevent axial air leakage betweenthem; and it is noted that and the catcher plates do not normally bearradially on each other or the front and rear bulkheads.

Although the embodiment shown in the majority of the drawings has only asingle antifreeze/methanol injection point radially outside the matrixof tubes 120, it is envisaged that a flight-ready engine may have atleast two injection points at different radial locations or more radiallocations as shown in FIG. 18 .

The transition tubes 702 shown in FIG. 9B may be useful in test rigs andmay be removed in operational engines.

The concave dished pockets in the catcher elements 126 are approximately50 mm long. The mesh 258 is wrapped tightly around the catcher tubes andsecured to them. This forms 50 mm long pockets where each catcher tube126 is dished, separated by the lands 254 where the mesh 258 contactsthe tube so as to compartmentalise the suction cavities into separatepockets so that in case of screen damage remaining pockets remainoperational.

The temperature control components including the temperature sensor 350and controller 352 may be adapted or replaced in other embodiments withother apparatus known to the skilled person in the art form maintaininga constant airside temperature profile for frost control by providingthe correct amount of methanol/water condensation at the particularcatcher locations. The control in at least some embodiments is adaptedto control the last (coldest) catcher row to be located at about -80 to-100° C. air temperature where the methanol concentration should beabout 80% mole fraction or 88% mass fraction to delay the freezing pointto the lowest possible temperature.

The frost control system requires very little consumable materialscompared to the previous publications mentioned above, i.e. the mass ofmethanol required is very low, translating into increased vehiclepayload and improved economics.

The connection of the methanol manifold 174 to the spokes 536 ispreferably via slotted holes (not shown) to allow for radial thermalexpansion.

The methanol injector ring 174 shown in the drawings is composed ofactive injection tubes 710 with alternate plain non-fluid injectingtubes 712 of larger diameter. This arrangement provides increased airvelocity close to the injection tubes 710 but the plain tubes 712 may beremoved in other embodiments.

The light pressing of the outlet headers 110 against the matrix of tubes120 using the springs 542 applies an initial preload which is augmentedby the airside pressure drop when the engine is running and it alsoprevents the module spirals 108 from swinging open when the axis of theheat exchanger 52 is horizontal. The helium bypass controls, 350,352,354may be replaced in other embodiments and the circuitry may be changed toinclude a recirculation loop and for alternative designs of catchertemperature control.

The heat exchanger may be used in other applications than with theengine shown and is not limited to use in the particular aerospaceapplication described and may be used in various other aerospace andindustrial applications.

Various features shown in the drawings may be varied to what is shownand described without departing from the scope of the invention. Forexample the end walls formed by the catcher plates 127 and bulkheads530,532 may be in other embodiments formed in thin sheet material.

In embodiments with generally radially outward air flow (inside ofradially inward), the tube support structure including the bird cagedrum 84 and I-beams 130 may be reversed such that the drum 84 ispositioned radially outside the spiral tubes 120 so as to resist outwardloading thereon.

In situations where the fluid (such as air) being cooled does notcontain water vapor, or if the fluid will not be cooled below 0 degrees,there is a relatively low likelihood that frost formation will impedethe operation of the heat exchanger. In such situations, it may beadvantageous to eliminate the frost control apparatus (e.g., themethanol injection system, the catcher assemblies 240, the shims 500,the doglegs 112′,114′, I-beams 130 in the region of the spiral sections108, arcuate pockets 160, radial portions 122 and foils/joggles 124)from the heat exchanger, to, for example, reduce weight when the heatexchanger is used with an engine (such as the engine disclosed in GB1318111.0).

Various modifications may be made to the described embodiments withoutdeparting from the scope of the invention as defined by the accompanyingclaims.

1-73. (canceled)
 74. A heat exchanger for cooling a fluid in a flow pathand containing a component liable to phase change below a temperaturethereof, the heat exchanger comprising a series of tubes for the passageof coolant and an injector for introducing an anti-freeze component intothe fluid in the flow path.
 75. A heat exchanger as claimed in claim 74,wherein the injector comprises an antifreeze injector, wherein theantifreeze injector comprises a methanol injector arranged forconnection to a source of methanol.
 76. A heat exchanger as claimed inclaim 75, further comprising a removal arrangement for removing liquidlocated within a body of moving fluid within the flow path.
 77. A heatexchanger as claimed in claim 76, wherein the removal arrangement islocated downstream of the injector.
 78. A heat exchanger as claimed inclaim 76, wherein the removal arrangement comprises at least one catcherelement arranged to extend generally transverse to a general flowdirection of the fluid therepast.
 79. A heat exchanger as claimed inclaim 78, comprising at least one row of said catcher elements.
 80. Aheat exchanger as claimed in claim 79, wherein the catcher elements arespaced apart in the row by a spacing distance which is less than themaximum cross-dimension of each said catcher element in the direction ofspacing.
 81. A heat exchanger as claimed in claim 80, wherein thespacing distance is about one quarter, one third or half of said maximumcross-dimension.
 82. A heat exchanger as claimed in claim 80, whereinthe catcher arrangement comprises a second row of catcher elements, thesecond row of catcher elements being staggered, in a direction from onecatcher element to another along a row, with the first row of catcherelements.
 83. A heat exchanger as claimed in claim 82, wherein thecatcher elements in the first and second rows are spaced from thecatcher elements in the same row substantially the same distance thatthey are spaced from the catcher elements in the other row.
 84. A heatexchanger as claimed in claim 78, wherein the at least one catcherelement has a longitudinal extent and has at least one point therealonga substantially circular cross section.
 85. A heat exchanger as claimedin claim 84, wherein the at least one catcher element comprises a hollowtube having at least one liquid collection pocket located on an exteriorsurface thereof.
 86. A heat exchanger as claimed in claim 85, whereinthe hollow tube is hydroformed of metallic material.
 87. A heatexchanger as claimed in claim 85, wherein the at least one liquidcollection pocket comprises a scavenge aperture communicating from theliquid collection pocket into an interior conduit of the hollow tube,the scavenge aperture area being of small size for limiting airflowdrawn thereinto with liquid.
 88. A heat exchanger as claimed in claim85, further comprising a mesh covering the at least one liquidcollection pocket, with a cavity formed between the pocket and the mesh.89. A heat exchanger as claimed in claim 88, wherein the mesh is anapproximately 25 micron to 100 micron mesh.
 90. A heat exchanger asclaimed in claim 88, wherein the mesh is coated with a wetting agent.91. A heat exchanger as claimed in claim 89, wherein the mesh isgenerally flat in the region of each pocket.
 92. A heat exchanger asclaimed in claim 85, further comprising a suction system fluidlyconnected to the hollow tube for removing liquid from the at least oneliquid collection pocket.
 93. A heat exchanger as claimed in claim 76,further comprising a second removal arrangement which is locateddownstream of said removal arrangement.
 94. A heat exchanger as claimedin claim 93, wherein the antifreeze injector comprises a plurality ofinjection portions and is arranged to inject a more concentratedantifreeze at a first injection portion in a first region of air flowand a more water-diluted antifreeze at a second injection portion whichis more upstream than the first injection portion at a second region ofair flow that is warmer than the first region.
 95. A heat exchanger asclaimed in claim 94, further comprising a recycle path for recyclingantifreeze and liquid water removed from air flow at the second removalarrangement for re-injection, upstream of the first removal arrangement,at the second injection portion, wherein each such re-injection in aplural sequence of such re-injections having the antifreeze more dilute,into warmer air and more upstream in the airflow than upon the previousinjection, the antifreeze being re-injectable along a sequence ofre-injection points along a path that is counter to the direction of airflow through the heat exchanger.
 96. A heat exchanger as claimed inclaim 74, which is adapted to cool air to below 0° C.
 97. A heatexchanger as claimed in claim 78, which is adapted to cool air to or tobelow about minus 100° C.
 98. A heat exchanger as claimed in claim 97,further comprising a control for controlling the environment in thevicinity of the coldest catcher element to be about 80 mol % or about 88wt % methanol, on a water-methanol solid-liquid phase diagram, astemperature approaches about minus 100° C.
 100. A heat exchanger asclaimed in claim 78, wherein the removal arrangement comprises asufficient number of catcher elements to remove over 90% of watercontent from air passing through the heat exchanger. 101-111. (canceled)112. An engine, comprising a combustion section and a heat exchanger asclaimed in claim 75, wherein the heat exchanger is adapted to cool airin a flow path directed towards the combustion section.
 113. An engineas claimed in claim 112, further comprising a helium supply forproviding helium as coolant flowable through the heat exchanger.
 114. Aflying machine, comprising a heat exchanger as claimed in claim
 75. 115.(canceled)